A mixing adjusting thermostatic water valve has been disclosed in the Chinese patent journal (Publication No.: CN101070925), which employs a geared motor or a step motor as a rotation driver to rotate a water temperature adjusting block provided with soft sealed pads on both sides thereof in such a manner that the soft sealed pads on both sides of the adjusting block can be attached to a cold water adjusting port and a hot water adjusting port, respectively, so as to adjust an outlet water temperature after mixture. The mixing adjusting thermostatic water valve has advantages of a simple process, a large flow rate, a reduced power, a quick and smooth temperature adjustment, a temperature difference equal to zero between the inlet temperature and the outlet temperature, and a small volume due to a mixing water chamber provided therein. However, when the pressure difference between the cold water and the hot water as well as the fluctuation of pressure difference are relatively large, for example, when the instant pressure difference goes up to 0.1 Mpa or so, the mixing adjusting thermostatic water valve will suffer from instant cross flow of the cold and hot water such that the thermostatic speed is reduced. When the pressure difference between the cold and hot water is increased to higher than 0.3 Mpa, the thermostatic effect will hardly be achieved. It is provided, for the case that the hot water is centrally supplied, the hot water must be turned off or nearly turned off in a short time when the cold water supplying is stopped, so as to avoid scalding accident. However, the above mentioned patent will be difficult to realize the above requirement when the hot water pressure is higher than 0.3 Mpa; moreover, after the hot water and power are turned off, the state that the hot water is turned off may still hardly be kept even when the hot water pressure is lower than 0.3 Mpa. When the mixing adjusting thermostatic water valve is applied in a volumetric electric water heater, a cold water inlet of the volumetric electric water heater is provided with a safety valve. The safety valve functions as a one-way valve with a certain pressure difference when the cold water flows into the volumetric electric water heater. The hot water in the volumetric electric water heater flows out of the water heater together with the cold water from the one-way valve in equal amount. A dynamic resistance of the hot water when flowing out of the hot water port of the volumetric electric water heater is equivalent to the pressure difference between 0.005-0.02 Mpa. The cold water is directly supplied by an inlet water pipe of the water heater. The pressure difference between the cold water and the hot water flowing into the thermostatic water valve is rapidly and frequently varied as the inlet water flow changes. The mixing adjusting thermostatic water valve will not be able to keep the outlet temperature constant due to the large fluctuation of the pressure difference of the cold and hot water.